My Math Forum  

Go Back   My Math Forum > College Math Forum > Applied Math

Applied Math Applied Math Forum

LinkBack Thread Tools Display Modes
August 12th, 2015, 08:02 AM   #1
Joined: Dec 2010

Posts: 19
Thanks: 0

How many triangles in this picture?

Hi, all.
I just thought of that kind of question and tried to count it.
Please see the picture below.

Finally got 42.
Can anyone help me confirm the answer, please?
Thank you very much.

Last edited by Kavesat; August 12th, 2015 at 08:04 AM.
Kavesat is offline  
August 12th, 2015, 08:37 AM   #2
Senior Member
mrtwhs's Avatar
Joined: Feb 2010

Posts: 704
Thanks: 138

I think I agree ... 42.

Call the lower left vertex A and the lower right vertex B. Then there are 30 triangles with A as vertex, 24 triangles with B as vertex and 12 triangles with AB as a side (that is, both A and B as vertices). By the inclusion-exclusion principle the total is 30 + 24 - 12 = 42.
mrtwhs is offline  
August 12th, 2015, 09:18 AM   #3
Global Moderator
Joined: Dec 2006

Posts: 20,373
Thanks: 2010

skipjack is offline  

  My Math Forum > College Math Forum > Applied Math

picture, triangles

Thread Tools
Display Modes

Similar Threads
Thread Thread Starter Forum Replies Last Post
picture goodfeeling Algebra 4 November 23rd, 2013 10:00 PM
How many discontinuities in this graph *picture attached* kahf1_01 Calculus 1 October 29th, 2011 09:52 AM
Picture Frame symmetry Algebra 4 October 3rd, 2011 02:41 AM
a picture question roflchopter Algebra 1 May 4th, 2011 07:42 PM
Solve for x, picture included hellxfire Calculus 2 May 14th, 2009 05:29 PM

Copyright © 2019 My Math Forum. All rights reserved.